The proposed work is directed at measuring the heterogeneous electron transfer kinetics for the reduction of three biological molecules; cytochrome c, myoglobin, and soluble ferredoxin, at solid electrode surfaces. These molecules were selected due to their physiological electron transfer roles (in the cases of cytochrome c and ferredoxin) and due to similar structures (cytochrome c and myoglobin are heme type proteins). The kinetics of electron transfer between these molecules and modified electrode surfaces are being measured using a spectroelectrochemical method (Albertson et al., Anal. Chem., 51 (1979) 556.). The modified gold electrode surface has also been previously described (Landrum et al., J. Am. Chem. Soc., 99 (1977) 3154). A considerable amount of work has been reported regarding the homogeneous electron transfer kinetics of these molecules, particularly in the case of cytochrome c. However, since this molecule and ferredoxin are believed to function physiologically in electron transfer with membrane bound species there is a need to understand the role played by the interface in these reactions. This study is being conducted to provide basic information about the heterogeneous kinetics associated with these selected molecules with the goal of contributing the understanding of the mechanisms of their reactions.